This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This multi-center double-blind placebo controlled trial will investigate the effect of vitamin D supplementation on the interferon signature in patients with systemic lupus erythmematosus (SLE). Vitamin D deficient patients with SLE who possess the interferon signature will be randomized to receive 0, 2000 or 4000 IU/daily of cholecalciferol (vitamin D3) for 12 weeks. Potential clinical effects as well as safety will be assessed and monitored.